O2 has announced it is going to try some VoIP services, under the brand of O2 Connect, while in America T-Mobile has opened up its Bobsled service to compete with Google Voice.

O2 Connect is just a trial run to see how the services work and how users react to them. The trial is invitation only, though those attending Wired 2011 (which starts today, in London) will be invited to take part. Those trialists will be able to make VoIP calls, and send text messages, from a smartphone over Wi-Fi, ahead of a commercial service which is expected next year.

Meanwhile, on the other side of the pond, T-Mobile recently updated its Bobsled service to enable everyone to make free calls to any phone number in the USA, or Canada, from anywhere in the world, as well as connecting up Facebook users on the move.

The problem with VoIP is how to charge for it, both technically (counting the calls securely) and dealing with the perception (created by Skype et al) that VoIP should be free. T-Mobile USA has addressed both those issues by handing out the service for free, though they'll probably be advertising at some point in the future.

O2 isn't saying how much it will charge for its VoIP service, though it is interesting to note that the operator plans to offer SMS over Wi-Fi, as well as voice connections, which is something other deployments have struggled with.

A free service is much easier in the USA where customers pay to receive calls (received calls are deducted from their allowed minutes). Such a service would be much more difficult in Europe where operators have to hand over a termination fee to the receiving network.

If O2 can provide reliable voice and messaging then it might provide an alternative to femtocells for in-building coverage. O2 ran extensive trials of femtocell technology a few years back, but decided against deployment, leaving Vodafone as the only operator in the UK using the technique (which is branded Sure Signal), with variable results.

But as voice traffic continues to rise, as voice revenue remains static, offloading some of that traffic onto the internet makes sense, even if it means giving the customers something for nothing. ®